1. Field of the Invention
The present invention relates to a wiring board wherein a wiring layer is formed on an insulation substrate comprising a core member and an organic resin, and particularly to a resin wiring board wherein a wiring layer is formed on a woven fabric as a core member which is impregnated with an organic resin.
2. Description of Related Art
Hitherto, a glass-epoxy insulation substrate has been generally used for a resin wiring board. As such wiring board, for example, a through-hole wiring board and a build-up wiring board can be exemplified. In an insulation substrate which is used for such a wiring board, a woven fabric or a non-woven fabric is used as a core member which is mainly made of glass fiber yarns and which was impregnated with an epoxy resin alone or an epoxy resin in which an inorganic filler is dispersed. By using such insulation substrate, the resulted wiring board has a sufficient stiffness, so that the wiring board becomes convenient to mounting for example, a passive part, a semiconductor package and so on. In addition, since the glass fibers have a good moisture absorption property, they lead to a good connection reliability in the wiring board.
With the development of an electronic part which is of a compact size, of a high performance and/or of an enhanced function, the wiring boards become compacted and densified. When the wiring board is densified, the number of electronic parts mounted on the wiring board is increased, and transmission of a high speed signal, particularly a high frequency signal is required to be transmitted in the wiring board. Upon such a requirement an insulation material which is used for the wiring board is requested to be improved in its dielectric properties (especially, a dielectric loss) so as to reduce a transmission loss. In order to meet such request, it is proposed to use an insulation substrate which comprises a woven glass fabric impregnated with a cyanate ester based resin, a polyphenylene ether resin or the like which has a lower transmission loss compared with a conventional epoxy resin (see, for example, Japanese Patent Kokai Publication No. 2001-339130).